As methods for reacting two phases of gas and liquid (gas-liquid two-phase) in a reaction column in which catalyst is accommodated, a downward co-current type or downflow type method (Japanese National Phase Laid-Open Patent Publication No. 2004-522567 (US2002/0076372)) in which the gas-liquid is flowed from top to bottom and reacted and an upward co-current type or upflow type method (JP-A 2003-176255 (US2003/0050510)) in which the gas-liquid is flowed from the bottom to the top and reacted are known. As a support body of catalyst used in these methods, a honeycomb structural body or a monolith structural body configured by a plurality of parallel narrow tubular channels is used since a pressure loss when fluid flows is small.
As a flow regime of the gas-liquid two-phase flow flowing through the narrow tubular channels configuring the honeycomb structural body, Taylor flow in which gas bubbles and liquid slug alternately flow is known. In the above-mentioned Taylor flow, since it is a very thin liquid film that separates the gas bubbles from the catalyst fixed on an inner wall of the channels, mass transfer between the gas and the solid wall is fast. Further, an internal circulating flow is generated in the liquid slug, and mass transfer inside the liquid slug is promoted as well. For these reasons, the honeycomb structural body is expected as a catalyst support body for a gas-liquid-solid catalyst reaction.
In the honeycomb structural body, since pressure loss is small, it is easy to apply an upflow type column as a reactor. In the upflow of the gas-liquid two-phase, since the liquid is in a continuous phase under a broad range of flow rates of the gas and the liquid, advantage that the flow in the narrow tubular channels in the honeycomb easily becomes Taylor flow is obtained. Also, according to regularity of the channel structure, it is considered that the flow becomes uniform with respect to a cross-sectional surface of the honeycomb.
At present, however, it is known that gas bubbles tend to flow into only part of channels selectively and the flow becomes unstable so that the flow becomes non-uniform with respect to the cross-sectional surface of the honeycomb.
The flow state inside a reaction column can be evaluated from residence time distribution (Kenji Hashimoto: Reaction Engineering (Baifukan, 1993) pp. 179-197 [in Japanese] (Literature 1)). The residence time distribution is directed to a distribution of time in which the fluid flowing into the apparatus at a certain moment resides in the apparatus. The residence time distribution can be obtained by, for example, momentarily injecting a tracer into an apparatus via an inlet to measure concentration response (change in concentration) of the tracer at an outlet of the apparatus so as to normalize the concentration response as a probability density (impulse response method).
As a residence time distribution E(t), a completely mixed flow and a plug flow that are model flow states completely opposite to each other are known. The completely mixed flow is directed to a flow state model of a continuous stirred-tank reactor, namely a flow in which the fluid is momentarily mixed to be uniform in the reactor, while the plug flow is directed to a flow state model of a tubular reactor, namely a flow in which the fluid are not mixed at all in the flow direction in the reactor. Since these assumptions cannot be strictly probable, these two flows are referred to as ideal flows.
The actual flow takes an intermediate residence time distribution between the completely mixed flow and the plug flow. For example, a fact that the residence time distribution in the reaction column is close to that of the completely mixed flow indicates that the mixture of the fluid in the reaction column is noticeable, namely the flow inside the reaction column is noticeably turbulent. In the case of the gas-liquid two-phase flow, it is most probable that the completely mixed flow reflects an unstable flow state.
In the completely mixed flow, since a large portion of fluid is discharged from the reaction column in a noticeably short residence time, reaction is not sufficiently progressed inside the reaction column. Accordingly, problems may be caused with respect to reaction activity. In contrast, fluid that remains in the reaction column for a noticeably long residence time also coexists. At this time, there is an increased possibility that the reaction is overperformed, not resulting in an intended product, but side products. That is, this may cause disadvantage on the selectivity of the reaction.
As researches in which the residence time distribution of the liquid is examined with respect to the upflow of the gas-liquid two-phase in the apparatus that accommodates the honeycomb structural body or the monolith structural body, Koei Kawakami, Kimihiro Adachi, Norimichi Minemura, Koichiro Kusunoki; Kagaku Kogaku Ronbunshu, Vol. 13 (1987) 318 [in Japanese] (K. Kawakami, K. Kawasaki, F. Shiraishi, K. Kusunoki; Ind. Eng. Chem. Res. 28 (1989) 394) (Literature 2), R. H. Patrick, T. Klindera, L. L. Crynes, R. L. Cerro, M. A. Abraham; AIChE J. 41 (1995) 649 (Literature 3), and T. C. Thulasidas, M. A. Abraham, R. L. Cerro; Chem. Eng. Sci. 54 (1999) 61 (Literature 4) are known.
In Literature 2, a monolith with 80 channels per square inch (80 cpsi, 12.4 per 1 cm2), which is configured by narrow tubular channels with a square cross section of width of 2.4 mm, is used. The monolith has a square cross section with each side of 2 cm and has a height of 10 cm (the number of the narrow tubular channels is 49). One or three of the monoliths are accommodated in a rectangular tube with a square cross section of each side of 2.2 cm. Stainless narrow tubes are inserted into all of the 49 narrow tubular channels so that the gas is uniformly dispersed. The gas is supplied through these stainless narrow tubes. The residence time distribution of the liquid obtained as mentioned above is close to substantially the completely mixed flow. The experimental condition seems that the superficial gas velocity is equal to or less than 5.2 ×10−2 m/s and the superficial liquid velocity is equal to or less than 5.2×10−4 m/s. The superficial velocity is obtained by dividing the flow rate by the cross-sectional area of the column (or the apparatus, reactor).
In Literature 3, a cylindrical tube with an inner diameter of 5 cm accommodates three monoliths (400 cpsi) each configured by narrow tubular channels with a width of 1 mm. The height of total of the three monoliths is 0.33 m. The narrow tubular channels between the monoliths are not consistent with each other. The residence time distribution of the liquid at the superficial gas velocity of 2.2×10−2 m/s and the superficial liquid velocity of 2.3×10−3 m/s is obtained, and the flow is close to the completely mixed flow.
In Literature 4, the monolith is emulated by bundling the narrow tubes (a height of 15.2 cm) having a square cross section with a width of 2 mm. The residence time distribution of the liquid at the superficial gas velocity of 1.2×10−2 m/s and the superficial liquid velocity of 1.2×10−3 m/s is obtained, and the flow is close to the completely mixed flow as expected. Here, the superficial velocity is calculated from device cross-sectional surface of 5.7 cm×2.3 cm.
As described above, with respect to the upflow of the gas-liquid two-phase in the apparatus that accommodates the honeycomb structural body or the monolith structural body therein, only the residence time distribution of the liquid that is close to that of the completely mixed flow is known.
In M. T. Kreutzer, J. J. W. Bakker, F. Kapteijn, J. A. Moulijn; Ind. Eng. Chem. Res. 44 (2005) 4898 (Literature 5) and A. Cybulski, J. A. Moulijn (eds.); Structured Catalysts and Reactors, Second Edition (CRC Press, 2006) pp. 426-427 (Literature 6), stability analysis of the flow is performed on the basis of the pressure loss model of Taylor flow in the narrow tubular channels. According to them, in the upflow, the flow becomes unstable irrespective of the flow rate conditions of the gas or the liquid. This is consistent with the result of Literatures 2 to 4.
In A. J. Sederman, J. J. Heras, M. D. Mantle, L. F. Gladden; Catal. Today 128 (2007) 3 (Literature 7), the upflow of the gas-liquid two-phase in the honeycomb is confirmed according to visualization by MRI. The monolith currently used is configured by narrow tubular channels with a square cross section of width of 1.7 mm, and the diameter of the monolith is 42 mm, and the height thereof is 0.15 m, and 200 cpsi. The monolith is accommodated in a circular tube having an inner diameter of 50 mm with a lateral surface sealed so that the flow is not bypassed. For example, velocity distribution of the liquid in the monolith cross-sectional surface obtained at the superficial gas velocity of 9×10−4 m/s and the superficial liquid velocity of 4.1×10−3 m/s is noticeably broad distribution also including downward velocity. This result is also consistent with the Literatures 2 to 6.
As described above, the upflow of the gas-liquid two-phase in the honeycomb packed column in which the honeycomb structural bodies are accommodated is unstable, and only the residence time distribution of the liquid that is close to that of the completely mixed flow is known. Therefore, in the honeycomb packed column, as can be seen in Japanese National-Phase Laid-Open Patent Publication No. 2004-522567 (US2002/0076372) and Literature 5, many studies are performed on the downflow.
Since the liquid dispersion is important in the downflow, in Japanese National-Phase Laid-Open Patent Publication No. 2004-522567 (US2002/0076372), the honeycomb structural bodies are shifted and stacked with each other to disperse the liquid. In Literature 5, a spray nozzle and a static mixer are used.
Also, as for the upflow, a method for dispersing the gas-liquid by a static mixer, for example, is disclosed as in JP-A2003-176255 (US2003/0050510). As disclosed in Literature 2, it is known that the residence time distribution of the liquid is close to that of the completely mixed flow even if gas dispersion is improved. Although mass transfer is promoted by the gas-liquid dispersion by the static mixer to increase the reaction efficiency in JP-A 2003-176255 (US2003/0050510), the flow state is not necessarily stable.
Further, one of the problems of a fixed-bed reaction column which is used as a reactor is to reduce the work load necessary for regularly exchanging the catalyst, and reduce costs including expenses for the work loads. To reduce the work load, a method for accommodating the catalyst in a container and packing the container in the reaction column may be applied. JP-A 2009-291695 discloses a configuration in which film catalyst obtained by stacking a corrugated plate film and a flat plate film alternately to be honeycomb structural body is accommodated in a cylindrical case.
When loading the container that accommodates the catalyst therein in the reaction column, clearance is often present between the inner wall surface of the reaction column and the catalyst container. In some cases, the clearance is generated due to dimension accuracy error upon manufacturing, while in some cases, adjustment is performed so that the clearance is formed in advance to facilitate the catalyst container to be taken in and out.
When the clearance is present in the reaction column, however, problems that the clearance becomes a bypass so that the reactant passes through the clearance without passing through the catalyst portion are caused. When reaction substances are two-phase of the gas and the liquid, in the upflow reaction column in which the gas and the liquid enters the reaction column from a bottom thereof and are discharged via a top thereof, in most cases, the liquid is in a continuous phase and the gas is in a dispersed phase where the gas is present as bubbles. In such cases, the bypass flow is in particular noticeable.
In order to restrict or suppress the bypass flow to the clearances, a method for using seal materials at portions corresponding to an inlet and an outlet of the clearance to prevent the gas and the liquid from flowing into the clearance is known. When performing the reaction over a long period of time, however, it is not easy to maintain sealing by the seal materials. Although there is a method for embedding the whole clearance with the seal materials, the work load is heavy and eventually the work load for exchanging the catalyst is heavy as well.
US2004/0120871 discloses a method for filling catalyst particles in a gap (clearance) between the reaction column and the monolith catalysts with respect to the integral monolith catalysts with a honeycomb structure. As for the monolith catalyst here, the accommodating container is not used. As well as the use of the accommodating container, however, it is intended to reduce the work loads for exchanging the catalysts.
Although it is considered that the bypass flow into the clearance is restricted by filling up the clearance with the catalyst particles, the filling work or the exchanging work of the catalyst particles itself results in an increase of the work loads.
Further, it is considered that, according to this method, a size or filling density of the catalyst particles to appropriately restrict the bypass flow into the clearance is unclear and thus, the control of the restriction is difficult. It can be considered that since the fillings in the clearance are also catalysts, a problem is not serious even if the bypass flow is present. A fact that the flow into the monolith catalyst to be utilized is reduced, however, is problematic for an efficient use of the catalyst.
Although Chemical Engineering Handbook, Sixth Edition (Maruzen, 1999) edited by the Society of Chemical Engineers, Japan: pp. 611-612 [in Japanese] (Literature 8) is not directed to control techniques of the bypass flow into the clearance, it discloses an internal loop airlift bubble column. Literature 8 discloses that a dual tubular structure is formed in the column, and by guiding the gas into an inner tube, for example, the liquid is accompanied by the gas so as to cause an upflow in the inner tube and a downflow in an outer tube.